Chucking fixture for connecting a tool head and a tool holder to machine tools

ABSTRACT

A clamping device for connecting a toolhead and a toolholder on machine tools using a cylindrical or at least partly conical location hole with corresponding shank, wherein a rotatable clamping bolt with spiral guides is used, in clamping to move clamping members outwards from within, thus providing a positive and non-positive locking of the toolhead and the toolholder. The clamping bolt has at least one stop to limit the angle of rotation in clamping. The retainer for the clamping members is spring mounted in the toolholder.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national phase of PCT/DE 94 01 337 filed 8 Nov.1994 and based, in turn, upon German national application P43 38 953.8of 15 Nov. 1993 under the International Convention.

The invention relates to a chucking fixture for connecting a tool headand a tool holder to a machine tool via a cylindrical or at leastpartially conical location hole and a correspondingly shaped centeringpin, wherein chucking elements can be moved from the inside to theoutside of recesses during the chucking process by means of a rotatablechucking shaft equipped with helical guides, whereby the tool head andthe tool holder can be secured by means of friction and positiveinterlocks.

BACKGROUND OF THE INVENTION

A chucking fixture of the type described is disclosed in EP 0 369 211B1. Only a very short chuck travel is required for chucking, whereby thetravel of the chucking elements is initially relatively large due to asteep inclination of the chucking cams, while the high chucking forcesrequired are applied in a second, substantially flatter portion of thechuck cam.

DE 35 24 739 A1 discloses a chucking fixture with a conical shank for atool holder, which tool holder is detachably arranged in a conicallocation hole of a tapered socket fastened in a chucking cylinder. Thelocation hole has a groove into which balls can be inserted as chuckingelements by means of a pull ring to which an axial pressure can beapplied, this ring being arranged slidably in a tapered socket. A stopring is located at the back section of the tapered socket so that therear position of the pull ring can be fixed by means of a stud. Betweenthis stop ring and an additional stop ring for the back section of thetie rod, there is a pressure spring for moving the pull ring and the tierod in axial direction. A ring through which the tie rod can pass andagainst which the pressure spring is braced serves this purpose. Thedisadvantage of the above-described fixture is its costly and complexdesign.

OBJECT OF THE INVENTION

The object of the present invention is to provide a chucking fixture ofthe type described in the introduction so that even with short chucktravel and a compact design, secure chucking is possible even when theparts of the chucking fixture have dimensions which deviatesignificantly from the nominal dimensions for which the device isintended.

SUMMARY OF THE INVENTION

This object is achieved by means of a chucking fixture of the typegenerally described above, but wherein the chucking shaft has at leastone stop to limit the angle of rotation during chucking and the holderfor the chucking elements is elastically prestressed in the tool holder.Due to this preliminary stress, the holder can deflect axially duringchucking, compensating for dimensional irregularities of the parts ofthe chucking fixture. The stop is a simple means to prevent damaging ofthe chucking elements, which is always a risk when chucking a toolwithout the use of a torque wrench or if excessive chucking force isapplied.

The holder for the chucking elements is preferably prestressed by meansof a tension spring, in particular a Belleville spring washer or packetof Belleville spring washers. Because of their low friction, balls arewell-suited for use as chucking elements, which are arranged in acanister as a holder. A compact design can be achieved, when thechucking shaft is located in a bore in the tool holder, orientedradially with respect to the common longitudinal axis of the locationhole and the centering pivot in the tool holder.

There are a number of possibilities for the limit stop. The chuckingshaft can have a head having a semicircular groove cut into its outsidesurface, in which groove the pin of the tool holder is guided so thatthe end faces of the groove represent stops to define the angle ofrotation of the chucking shaft. Alternately, the guide of the chuckingshaft for the chucking elements can have a dome-shaped trough or troughswhose radius/radii has/have been modified to correspond to the shapes ofthe chucking elements. As soon as a certain angle of rotation isreached, the ball falls into such a trough, which occurrence can easilybe detected by the operator. Under these conditions it is impossible toinadvertently overtorque the chucking shaft.

It is preferable and is also known in principle from the prior art thatthe holder for the chucking elements can be secured against rotationrelative to the tool holder. In one particular embodiment of theinvention a pin is used as protection against rotation.

Because tool heads often remain stuck in the tool holder after machininga workpiece, or are fitted in a self-locking manner in the tool holderby means of the design of a conical recess in the centering pivot, it isnecessary to use an ejector to remove the tool head. The inventionincludes a chucking shaft configuration with a second helical guide bymeans of which the ejector can be actuated.

To reduce chucking time, the guides are restricted to an angle ofrotation of 20° to 160°. The angle of rotation is understood as theangle by which the chucking shaft must be rotated to chuck or releasethe tool head. The guides are appropriately located along the outersurface of the chucking shaft, preferably with an angle of rotation of115°.

According to another embodiment of the invention, the guides describe acontinuous second order or higher three-dimensional curve, whoseslope--in relation to the tool chucking process or ejection--steadilydecreases, preferably hyperbolically, exponentially or logarithmically.The mentioned embodiments can be used so that by means of a relativelysteep inclination of the chucking cam, a slight movement of the chuck atthe beginning results in a correspondingly large amount of travel of thechucking elements and the requisite high chucking forces can increasesharply in a subsequent, significantly flatter section. The same appliesto ejection, where high forces are required initially, before there issignificantly greater chuck travel after overcoming the static friction.

Finally, the recess for the centering pivot of the tool head is realizedas a bore or an annular groove for the chucking balls and/or one sidesurface is realized as a bevel.

According to another embodiment of the invention, the guides have anapex point (dead point) whereby until this point is reached during thechucking process, the chucking elements are displaced increasinglyradially outward and when this point is passed, the balls move intochucking position.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features, and advantages will become morereadily apparent from the following description, reference being made tothe accompanying drawing in which:

FIG. 1 is a cross section through the tool holder;

FIG. 1a is a side new partly in section through a tool holder and a toolhead;

FIG. 2 is a side view of a chucking shaft;

FIG. 3 is a cross section along the line III--III of FIG. 2; and

FIG. 4 is a cross section through a tool holder with elastic moldedelements.

SPECIFIC DESCRIPTION

The tool holder 10 shown in FIG. 1 has a conical shaft 11 for mountingon a machine tool, a rotating disk or the like. The tool holder has aconical seating bore, hole or socket 12 in which a correspondinglyshaped centering pin of a tool can be inserted. The ring-shaped stopcollar of the tool rests at 13 against the tool holder. The chuckingfixture consists of a radially oriented chucking shaft 14, which isshown in greater detail in FIGS. 2 and 3. This chucking shaft has a head15 into whose outer surface a groove 16 extending over an angle of 115°is cut. This groove serves as a guide for a pin 17 connected to the toolholder, whereby the respective end faces of the groove 16 serve as stopsto limit the angle of rotation of the chucking shaft 14. The chuckingshaft which can be rotated about its longitudinal axis 18 has a spiralchucking and ejection path 19 on its surface, the course of which can beseen in greater detail in FIG. 3. Due to these spiral guides 19, whichare essentially second order or higher three-dimensional curves, a shortchucking motion will move the chuck a relatively long way at thebeginning of chucking, as a result of the relatively steep inclination.20 indicates the initial position wherein the locating face of theholder is in contact with the corresponding ring-shaped locating face ofthe tool head. The chucking ball reaches its highest position 22 whenthe chucking shaft is rotated around the longitudinal axis (see arrow21) and moves past this point to the chucked position 23, whereby in thelast part of the curve, i.e. from position 22 to position 23, thechucking distances are clearly shorter, so that great force can beapplied here. When loosened, the chucking balls drop into the recesses24. The chucking shaft can be actuated by means of a key inserted intohex socket 25. The tool base holder 10 also has a holder, retainer orcanister 26 for the chucking balls (not shown), which holder issupported by means of a packet of Belleville spring washers 27, bracedon one side against a ring 28 and the head 29 of a screw rigidlyconnected to the canister 26. The springs 27 exert a tensile force onthe holder 26 in the direction of arrow 30.

Instead of a stop realized by means of a groove 16 in combination with apin 17, there can also be a dome-shaped recess 31 in the chucking cam19, as suggested in the left half of FIG. 3. During chucking theoperator notices a significant decrease in the force counteracting thechucking movement as soon as the ball drops into the chucking positionin the dome. Therefore the operator can also recognize (i.e. withoutstops) when the chucking position has been reached.

The advantage of the current invention lies in the fact that the holder26 can deflect axially against the force of spring 27 during chucking,so that the chucking fixture is protected against damage, even in theevent of manufacturing inaccuracies. The dimensional tolerances cantherefore be somewhat larger; in some cases, tolerances of up to 5/10 mmare acceptable. By means of the holder 26, to which prestress is appliedby means of springs, together with insertion of the chucking shaft 14 inthe radial bore of the holder, a compact structure with great stiffnesscan be accomplished. The spring resistance used depends on the size ofthe tool holder and can be as high as 4 metric tons. Naturally, a coilspring which engages in a helical groove in the holder 26 and whose freeend is rigidly fastened to the body of the tool base holder by means ofa bolt or similar fastener, can be used instead of the Belleville springwashers 27.

According to one embodiment of the invention, the chucking andloosening/ejection process can be carried out with only one chuckingcam. This is possible only because of the special design of the chuckingcam on the chucking shaft and the spherical shape of the ejector.

The axial compliance of the holder (canister) is primarily necessary toensure that the upper dead point of the chucking cam is reached andpassed. The axial displacement of the holder makes it possible to avoidmechanical redundancy.

Also possible are flexible moldings (FIG. 4) which are rigidly connectedto the holder (canister) 26 or which form an integral component with theholder.

To relieve the tension or eject the tool head, the chucking shaft 14 isrotated in the direction opposite to the direction indicated by arrow21, so that the chucking balls are relieved of pressure due to thedecreasing inclination of the chucking cams 19 until reaching the endposition, defined by a stop in the groove 16 of the head 15, and theballs drop into the recesses 24.

During loosening a somewhat greater amount of torque (release moment)must initially be applied to overcome the highest position of thechucking cam 19. This greater torque simultaneously represents goodprotection against unintentional loosening of the chuck, such as due tovibrations.

The actual ejection of the tool head is achieved by means of theinteraction of the steep portion of the chucking cam 19 shown in thelower left region of FIG. 3 with the spherical compression piece 33 ofthe ejector 32, when the chucking shaft 14 is rotated in the directionopposite to the direction indicated by arrow 21. As soon as the highestpoint 22 of the chucking cam 19 passes the compression piece 32 at thespherically shaped end, the compression piece 32 achieves the maximumvalue for the direction of ejection 34, which is sized so that the toolhead is safely ejected.

The guides of the chucking shaft are described in detail in EP 0 369 211B1 (see also U.S. Pat. No. 4,981,057), to which express reference ismade.

We claim:
 1. A chucking fixture for connecting a tool body to a machinetool, comprising:an elongated tool holder having a longitudinal axis, ashaft at one end receivable in a machine tool and a location hole formedin said tool holder, centered on said axis and open at an opposite endof said tool holder, said location hole being at least partly of conicalconfiguration, whereby a centering pin of a tool body is receivable inand centered in said hole; a plurality of chucking elements in said toolholder engageable with said tool body for locking said tool body in saidtool holder; a retainer in said tool holder and in which said chuckingelements are received, said retainer being axially movable in said toolholder toward and away from a mouth of said location hole; means in saidtool holder for elastically prestressing said retainer relative to axialmovement in said tool holder; a chucking shaft extending radially ofsaid longitudinal axis in said tool holder and into said retainer forengagement with said chucking elements, said chucking shaft beingrotatable about a radial axis of said tool holder and having spiralguide surfaces for camming said chucking elements outwardly with respectto said longitudinal axis to lock said tool body in said tool holder;and stop means for limiting rotation of said chucking shaft about saidradial axis.
 2. The chucking fixture defined in claim 1 wherein saidmeans in said tool holder for elastically prestressing said retainerrelative to axial movement in said tool holder includes a stack ofBelleville spring washers acting upon said retainer.
 3. The chuckingfixture defined in claim 2 wherein said chucking elements are balls. 4.The chucking fixture defined in claim 3 wherein said chucking shaft hasa chucking shaft head, said stop means including an arcuate grooveformed in said chucking shaft head and a pin projecting from said toolholder into said arcuate groove.
 5. The chucking fixture defined inclaim 4, further comprising an ejector movably received in said retainerand engageable against said tool body upon rotation of said chuckingshaft to release said tool body.
 6. The chucking fixture defined inclaim 4 wherein said arcuate groove is constructed and arranged topermit rotation of said chucking shaft through 20° to 160°.
 7. Thechucking fixture defined in clam 6 wherein said chucking shaft has apair of spiral camming surfaces separated by recesses receiving saidballs for release of said tool body from said tool holder.